Dental caries is the single most common affliction across the globe, affecting 2.4 billion people. The current process of identifying dental caries involves examining caries formation by naked eyes or X-ray during routine checkups. Once identified, surgical-restorative procedures are used to drill out the decay portion of the tooth an filled with synthetic material. This style of 'drill & fill' dental care is highly ineffective and osts more than $43 billion in the United State per year. The American Dental Association promotes the early detection and preventive treatment paradigm, which could dramatically reduce human suffering and the high cost associated with the disease. Traditional broad spectrum compounds such as chlorhexidine and Xylitol are effective, however even more promising are species-specific antibiotics which leave the 'healthy' commensal bacteria intact. For these preventive treatments to be useful, it is crucial that caries formation is predicted before structual damage is done to the tooth. We propose to achieve that by detecting Streptocauccus mutans (S. mutans), a major cariogenic bacteria which its salivary concentration strongly correlates to future caries formation. Currently, the only methods capable of detecting S. mutans at relevant concentrations are all lab based, such as PCR or ELISA, which are very rarely used due to the high cost and long time-to-result. The main goal of this project is to develop the next generation rapid, inexpensive and simple test for the detection of S. mutans using the novel 3-dimensional Paper Sensor (3PS) technology. The 3PS device incorporate a sample pre-concentration step using aqueous two-phase system (ATPS) and a rapid lateral-flow immunoassay (LFA) for detection. Traditional LFA is not sensitive enough to detect S. mutans at relevant concentrations. To overcome this barrier, a concentration component using ATPS can concentrate the target pathogen by several orders of magnitude prior to LFA detection. By using paper microfludics, we demonstrated our 3PS device can simultaneously and seamless concentrate and detect target pathogen using only light and inexpensive paper materials. Once fully developed, the 3PS device will be a rapid (<10 mins), inexpensive, and disposable diagnostic that dentists can use in the office to reliably predict caries formation at the chairsid. With this diagnostic, preventative treatment of caries formation becomes a practical solution for dental healthcare professionals. In Phase I, we will develop the prototypes of the 3PS device using 2 approaches: a low-hanging fruit two-stage platform, and a high-risk, high-reward one-stage platform. The successful execution of these aims will result in a diagnostic test that can predict caries development, allowing dental healthcare professionals to use preventive treatment rather than the current drilling & filling approach. This will drastically reduce the cst of dental caries treatment and improve the quality of care. The simplicity and cost effectiveness of this early detection and preventive treatment combination has the opportunity to revolutionize healthcare of dental caries both in industrialized and resource poor settings.